Loop antenna



Dec. 13, 1949 A. G. KAN DOIAN LOOP ANTENNA Filed Jan. 27, 1945 554 55e 542 54e 55o 554 ssa 562 56e 57o A DRA/EY Patented Dec. 13, 1949 UNITED sures- VArnlg' G. Kandoian,

New York, N. Y., assigner to `Federal. Telephone and Radio Corporation,l`

New YormN. Y., 'incorporation ofDelaware Appli-cation Januar-ym, 194s, seriaLNo. 5743732 (Cl. Z50-33) necessitating such feeding expedients as cross overs in the balanced feeder whichcarried the:

power to the radiating elements. rIhis cross over frequently was a major 'source of electrical' or mechanical troubles.

Another difficulty with the useo'floop antennas in the past has been the requirement for a balanc'ed line which is ordinarilymoreexpensive to manufactureand is less readily available thanethe simple coaxial line.

Further dimculties were experienced, in the degreetowhich a balance was required in the transmission and in the matching of the antenna impedance to that of the feeder. As a result 'or the a-boveprobleins rather complicated mechanical designs were frequently necessary'.

It is an object of the present invention to 'provide a loop antenna for frequency modulation and television purposes which is ei'cient overa relatively wide band ofhigh frequencies and which overcomes the above described diiiculti'es.

It is a lfurther cbect tia-provide a loop antenna whichvv is distinguished by the simplicity of its mechanical designand construction andy which lends itself-to an easy stacking of a large number offantenna uni-ts for the achievement of direc tivi'ty in an axial plane.

In accordance with the invention, I provide a suitable number of tubular circumferentially arranged magnetic dipolety-pe radiators which 'are fed inp'arallel from an axiallylocated junction point supplied by a common type coaxial transe mission line. Each 'of 'the radiators is vconmecfted t the C'a-Xil lille by means- OfY-an individua-1 coaxial vconducting' arm; all er which are eena nected in parallel with: respect 'to the. coaxial power supply feed line. One or: the features-of the invention is that vthe .radiators aswell as 'the supply arms` form part of the coaxial feeding system aswell as the; mechanical structure.V

These and other viieatuioes and objects of this invention will become .more apparent asy the infventi-on is described ingreater detail in connection with the. accompanying drawing;V wherein:

2. Fig. 1 is a perspective; view ofv the mechanical construction of, ai four element loop antenna in; accordance with my invention;

Fig. 2 is a schematic representation of a loon` antenna off' my; invention comprised of asingle;

' circular member, while Figs. 3: and 4v are schematic;

representationsY of four and' siX member. circularloops respectively;

Fig. 5 is ay graphi showing 'therelation between the standing wavearatio-andoperating frequency.' for a loop antenna in accordance with my-inven@ tion; and

Fig; 6 is a: schematicshowingv of an antenna arrayl employing a stack-i of fourv vertically are ranged loops.

Referring now. tothe drawing, vthe loop antennav of Fig. 1 is shown 'to -oomprisefour hollow tubular radiators I, 2, Sande, arranged in a quadrilaterali form.

These radiators which are preferably each a 1/2y wavelength long atfthe mid-.frequency of the operating band are fed coaxially and in Vparalleli: from a `common coaxialllfeeder line comprisedv of an inner'conduct'o'r 5 anda shield 6. Tlhe coaxial; line 5', 6 is coupled intov a junction box 1 into which arecoupledlfour coaxial conducting arms 8', 9, Il! and'll'l.' 1

These conducting arms :are similarly each comprised of an outer 'shield as well'V as. an inner: conductor I'2, #3.14, and I5 which are connectedA in parallel. tov the centrali conductor 5 of' thecc` axial feed line within thejunction box 1. The shields of' these arms are conductively coupled tov the shield ofthe coaxial line through the outside shield of the junction'` box 1'. The inner conV ductors I2; I3, i4 and Hi` continue toward the. center of'therespective radiating elements. and then each 'turnto one side- 'torun axially along' the inside of the radiators for 1K2 the length thereof as atY i6, 1.1., M3 and l'9toterminate in a conducting plate 20, 2l', 22', and 23 disposed inA thenear end of the succeeding radiatingelement; These radiatingi members arevseparatedfrom one another by shortgaps as 'at 24 between t'he open endoff one and-r the Vcl'cirsed end'ofl the adjacentradiators.

Other possible :forms of this type of antenna may be seen in Figs'. 2,., 3, and 4lwhere a circular form has been illustrated as embodied in single, four and six member loops.

The circumference-of the single-member loop is preferably inthe neighborhood of 1/2 wave-` length or less, the'multiplef imember'loops beingmadeup of substantially 1A; wavelengthv radiators.: Nol-imitations otherthan practical existiiorrthe number of members making up a loop. Thus a loop antenna of any diameter may be constructed and the old limitation of a diameter less than l/2 wavelength need not be observed in this case.

It is to be noted that all portions of the antenna. are metallic and form a mechanical supporting structure and that the radiators themselves form part ofthe coaxial feeding system. If the size of the unit is such that its own structure is not sufficient to carry the mechanical load, the antenna lends itself easily to the addition of suitable bracing members which may form part of the electrical system without affecting its characteristics.

The four connecting arms 8, 9, ID and II here function as impedance transformers between the feeder line of the radiators and are preferably made A or an odd multiple oi 1A wave long, their impedance being held low by choosing a large diameter axial conductor for at least the first 41 Wavelength thereof as at I2, I3, I4 and I5 in relation to the conducting portions I6, I'I', I8 and I9 within the radiators. These conducting arms may be connected to the tubular bodies of the radiating members by any known sheet metal fab' rication at a point of low or null voltage thereon so that the shield of the entire system may be put at ground potential and serve as a return conductor, thus obviating the requirements for insulators. These arms may also, when desired, be connected to the radiators on the inside thereof as indicated at 25, in Fig. 3. The arm, in this case, passed through an opening on the inside radius of the radiators and is attached by any desired means to the inside of the tubular conductor. The choice of these methods of connection is largely determined by the most favorable low voltage point on the radiator.

The connection of the transmission line to the radiators at the connecting plates 2li-23 constitutes an actual short circuit between the inner and outer conductors of the coaxial conducting system. The impedance at the gap between radiators is normally quite high when the radiators are made substantially M2 wavelength and low when the radiators are substantially 1,/11 wavelength. 'Ihe feeder within the radiator and also that within the supporting arm is made to have such a surge impedance as to match the centrally located main coaxial feeder. It is thus possible in the present type loop to obtain an antenna which is inherently matched to any common type of coaxial transmission line by the proper choice of surge impedanoes of the transmission line with-A in the connecting arms and the conductors Within the radiators Without any further matching being necessary as in some previous loop designs.` The radiation patterns of small loops of this type are well known and so far as the horizontal radiation is concerned, that is in the plane of the loop, the radiation pattern is substantially circular. The vertical radiation however, that is in the plane perpendicular to the loop, is a function of the diameter thereof. The vertical pattern of a loop whose diameter is any value d is given approximately by where K is a constant, I is a loop current, J1 is a Bessel function of the first order, A is the wavelength and B is a vertical angle, zero at the horizon. Highly directive patterns in the vertical plane may be obtained with this type of loop while retaining the omni-directional pattern in the horizontal plane. This may be done by vertical stacking of any desired number of loops. An example of this arrangement is shown in Fig. 6 wherein 26 is a transmitter; 21 a commercial type coaxial line; 28 a junction box and matching means; 29 is a 1A; Wave impedance transforming line; 30 and 3l are suitable portions of a coaxial feed line; and 32 are four vertically stacked loop antennas of the type hereinabove described.

In Fig. 5 the operating characteristic of a typical loop antenna constructed in accordance with my invention and operating over a useful range of frequencies as between 530 and 570 me., is shown as expressed in the relation between the standing wave ratio and operating frequency, the

, favorable wide band characteristic being immediately apparent.

It will be seen therefore from the above description that I have provided a loop type antenna which:

(a) Does not require balanced feeders;

(b) Does not require any stubs for matching and in which therefore the full band width capability of the loop may be realized;

(c) vDoes not require insulating mechanical supports;

(d) And which may be constructed to any desirable size diameter with essentially uniform current distribution.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention as set forth in the objects of my invention and the ac' companying claims.

I claim:

1. An antenna comprised of a given number of discrete tubular members arranged in a loop and acting in cooperation to produce translation of radiant energy, and an energy feeding line for said loop comprised of a first and a second conductor, said rst conductor lbeing connected to each of the said tubular members intermediate the end thereof and said second conductor being connected to a corresponding end of each of said members.

2. An antenna according to claim 1 wherein said number of radiating members is one.

3. An antenna according to claim 1 wherein said first conductor is connected to said tubular members at `a point of minimum voltage.

4. An antenna according to claim 1 wherein each of said members is substantially 1/a a wavelength long at the operating frequency.

5. An antenna according to claim 1 wherein said energy feeding line is a coaxial line and said rst and said second conductors comprise an outer shield and an axial conductor respectively.

6. An antenna comprised of a given number 0i hollow tubular members arranged in a loop and acting in cooperation to produce translation of radiant energy, each of said members having two ends and being substantially 1/2 a wavelength long, a coaxial energy feeding line for said loop having an outer shield and an inner axial conductor and coaxial impedance transforming means coupling each of said members at points intermediate their ends and said line, said means having an outer conducting shield connected to said first named shield and to said tubular members intermediate the ends thereof and an inner conductor connected to said axial conductor and an additional conductor connected between said inner conductor and a corresponding end of each of said members.

7. An antenna according to claim 6 wherein the said conducting shield of said transforming means is connected to said .tubular members at a point of minimum Voltage.

8. An antenna according to claim 6 wherein said additional conductor is yarranged axially inside a portion of one of said radiating members and is connected to another adjacent one of said radiating members.

9. An antenna comprising a plurality of discrete hollow tubular radiating members iarranged in a loop, a coaxial energy feeding line for said loop having an outer shield and an inner axial conductor, and coaxial impedance transforming arms coupling each of said members lat :points intermediate the ends thereof and said line, each of said impedance transforming arms having an outer shield and an inner axial conductor, said last named shield being connected to rst named shield and the corresponding member intermediate the ends of said member, and said last named axial conductor being connected to said first named axial conductor and an additional conductor connected -between said axial conductor and one en-d of a member adjacent to the member to which the corresponding shield is connected.

10. An antenna according to claim 9 wherein said additional conductor as extended is partly disposed Iwithin each of vsaid corresponding members.

11. An antenna according to claim 9, wherein said transforming arms are each 1A wavelength pair and in spaced relation thereto for interconnecting the other conductor of said transmission line and the next adjacent radiant acting member.

13. An antenna comprising a plurality of substantially horizontal radiant acting members each member having two interconnected elements, said members being arranged with their ends adjacent one another to deiine a substantially closed periphery, branch coaxial lines extending from the connection points of said elements to a common feeder point substantially symmetrically arranged within said periphery, the outer conductors of said branch lines being connected respectively to said members at the connection points of said elements, and a conductor arranged within one element of each member and connected 'at one end to the central conductor of its respective line and at the other end to the next adjacent member, a coaxial feeder line for supplying energy to and supporting the said antenna, and means for connecting the inner conductor of said coaxial line with the inner cond-uctors of said branch lines and the Outer conductor 0f said coaxial line `with the outer conductors of said branch lines at said feeder point.

ARMIG G. KANDOIAN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,127,088 Percival et al Aug. 16, 1938 2,167,709 Cork Aug. 1, 1939 2,187,014 Buschbeck Jan. 16, 1940 2,201,807 Berndt May 21, 1940 2,289,856 Alford July 14, 1942 2,293,136 Hampshire Aug. 18, 1942 2,383,490 Kfandoi'an Aug. 28, 1945 2,391,026 McGuigan Dec. 18, 1945 2,393,981 Fuchs Feb. 5, 1946 FOREIGN PATENTS Number Country Date 388,072 Germany Jan. 9, 1924 

